A standoff is underway between several members of John Wayne's family -- with his son and daughter battling each other over millions.
It's all over The Duke's estate -- worth somewhere between $10 and $15 million ... depending on which kid you ask.
In legal papers, filed Thursday in L.A. County Superior Court, John's daughter Aissa Wayne claims she wants to sell her share of the estate -- and another one of the The Duke's kids, Ethan Wayne, is obligated to come up with a "fair-market" price to buy her out.
Aissa -- along with several of Wayne's grandkids -- claim they believe the fortune is worth $15,400,000 ... but Ethan only thinks it's worth $10,704,000.
Now, Aissa -- and the grand kids -- want a judge to rule on the value of the estate ... so they can get their money and move on with their lives.